The present invention relates to an apparatus for forming a coating film for semiconductor processing, particularly, to an apparatus in which a thin plate-like substrate such as a semiconductor wafer or a substrate of a liquid crystal display (LCD) device is coated with a processing solution such as a photoresist solution or a developing solution for forming a coating film on the substrate. The term "semiconductor processing" noted above represents various treatments for forming a semiconductor device, wirings and electrodes, which are connected to a semiconductor device, etc. by forming predetermined patterns of a semiconductor layer, an insulating layer, a conductive layer, etc. on a semiconductor wafer, an LCD substrate, etc.
In the manufacture of a semiconductor device or an LCD device, an apparatus for forming a coating film is used in many cases. For example, the apparatus is used for forming a coating film by coating a substrate with a processing solution such as a photoresist solution or a developing solution.
FIGS. 1A to 1C are cross sectional views collectively showing a conventional apparatus for forming a coating film used in the manufacture of a semiconductor device or an LCD device. As shown in FIG. 1A, the apparatus, which is called a cap coater, comprises a tank 1 having a coating solution 2 housed therein. A nozzle 3 is arranged within the tank 1. These tank 1, coating solution 2 and nozzle 3 collectively constitute a coating solution supply means 4. The nozzle 3 is constructed to spurt upward the coating solution 2 to form a band-like upward stream. During operation of the apparatus, the height of the nozzle 3 is controlled as shown in FIG. 1B or FIG. 1C.
A substrate 6 such as a semiconductor wafer or an LCD substrate is held by a chuck plate 5 and arranged to face the nozzle 3. For forming a coating film on the substrate 6, the coating solution is supplied through the tip of the nozzle 3 onto the substrate 6, and the coating solution supply means 4 is moved in parallel and relative to the substrate 6, as shown in FIG. 1B.
In the apparatus shown in FIGS. 1A to 1C, the discharge port of the nozzle 3 can be made long in a direction perpendicular to the moving direction of the nozzle 3 such that band-like stream of the spurting solution covers the entire width of the substrate 6. In this case, a desired coating film can be formed by a single coating operation, making it possible to form the coating film promptly in a short time.
However, a coating apparatus used in the manufacture of a semiconductor device or an LCD device is required in recent years to be capable of forming a coating film of a uniform thickness, which does not contain cells, and is also required not to give impact to the substrate in addition to the capability of forming a coating film promptly in a short time. The conventional coating apparatus shown in FIGS. 1A to 1C is unable to meet the above-noted requirements.
An extensive research is being made in an attempt to meet the particular requirements. For example, disclosed in Japanese Patent Disclosure (Kokai) No. 4-124812 is a technical idea that a coating film is formed by using a nozzle constructed such that the discharge port, through which the coating solution is spurted upward to form a band-like stream, is connected to a coating solution reservoir via a plurality of fine tubes. Further, disclosed in Japanese Patent Disclosure No. 5-55133 is a technical idea that a coating film is formed by using a nozzle arranged above a spin chuck for holding a semiconductor wafer. In this case, the nozzle comprises a coating solution reservoir having a rectangular cross section and a plurality of fine holes made in the bottom portion of the reservoir. Still further, disclosed in Japanese Patent Disclosure No. 7-326554 is a coating film-forming apparatus comprising a nozzle for supplying a developing solution. The nozzle in this prior art includes a plurality of nozzle holes arranged in a bottom portion of a developing solution chamber and a pressure buffering member arranged in the vicinity of the nozzle holes for suppressing the pressure fluctuation of the developing solution.
The prior arts exemplified above teach that a coating film can be formed accurately on a substrate having a uniform thickness. However, a semiconductor wafer or an LCD substrate is not necessarily uniform in thickness.
FIG. 2 shows a cross section of a general substrate such as a semiconductor wafer or an LCD substrate. It should be noted that a thickness d.sub.1 at one end of a substrate 7 held by a chuck plate 10 differs from a thickness d.sub.2 at the other end of the substrate 7. Where the substrate 7 has a thickness of about, for example, 1 mm, the difference between d.sub.1 and d.sub.2 reaches as much as scores of microns in some cases. Where the substrate is not uniform in thickness, the distance at one end of the substrate between the discharge port of the nozzle and the coating surface of the substrate appreciably differs from that at the other end, even if the chuck plate for holding the substrate is held perfectly horizontal. In other words, it is impossible to maintain constant the distance between the nozzle and the substrate over the entire region of the substrate.
Where the distance between the discharge port of the nozzle and the coating surface of the substrate is not uniform, the coating solution fails to assume a uniform condition over the entire region of the substrate. The nonuniform condition does not bring about a problem in the case where subtle treatments are not required. When it comes to the manufacture of a semiconductor device or an LCD device, however, the coating film, e.g., a resist film, is as thin as about 1.5 to 2.0 .mu.m. On the other hand, the variation in the distance between the discharge port of the nozzle and the coating surface of the substrate is as much as scores of microns. It follows that, in the manufacture of a semiconductor device or an LCD device requiring subtle treatments, only a slight difference in the condition of the coating solution attached to the substrate greatly affects the uniformity of the coating film formed on the substrate. What should be noted is that a nonuniformity in the thickness of the substrate brings about a nonuniform thickness of the resultant coating film, leading to a low yield.